Executive Summary

[{'type': 'paragraph', 'content': "CVE-2026-27829 is a Server-Side Request Forgery (SSRF) vulnerability in the Astro web framework versions 9.0.0 through 9.5.3. It occurs because Astro's image pipeline does not enforce domain restrictions when using the inferSize option, which fetches remote images at render time to determine their dimensions."}, {'type': 'paragraph', 'content': 'Normally, Astro restricts remote image fetching to authorized domains specified by the image.domains or image.remotePatterns settings. However, when inferSize is enabled, no domain validation is performed, allowing the server to fetch images from any remote host regardless of these restrictions.'}, {'type': 'paragraph', 'content': 'An attacker who can control the image URL (for example, via CMS content or user input) can exploit this to make the server fetch content from unauthorized or internal hosts, bypassing the configured domain allowlist.'}] [1]

Useful 0 Not Useful 0

Impact Analysis

This vulnerability allows attackers to bypass domain restrictions and perform SSRF attacks, causing the server to make unauthorized requests to arbitrary hosts.

Potential impacts include accessing internal network services or cloud metadata endpoints that are normally protected, which can lead to unauthorized information disclosure or other malicious actions.

The vulnerability has a moderate severity with a CVSS v3 base score of 6.5, indicating it can affect integrity and availability to a low extent without requiring privileges or user interaction.

Useful 0 Not Useful 0

Compliance Impact

I don't know

Useful 0 Not Useful 0

Detection Guidance

This vulnerability can be detected by monitoring server logs for unexpected outbound requests to unauthorized or internal hosts, especially those triggered by image fetches during render time when the inferSize option is used.

A proof-of-concept involves configuring Astro to allow image fetching only from authorized domains and then checking if requests are still made to unauthorized internal services.

You can use network monitoring tools or commands to detect such unauthorized requests. For example:

• Use tcpdump or Wireshark to capture outgoing HTTP requests from the server and filter for requests to unexpected IP addresses or domains.
• Use curl or wget commands to test if the server fetches images from unauthorized hosts by manipulating image URLs in the application.
• Check application logs for image fetch requests that do not match the configured image.domains or image.remotePatterns.

Useful 0 Not Useful 0

Mitigation Strategies

The immediate mitigation step is to upgrade the @astrojs/node package to version 9.5.4 or later, where this vulnerability has been fixed.

Until the upgrade is applied, avoid using the inferSize option in the image pipeline, as it bypasses domain restrictions and enables SSRF.

Additionally, review and tighten the image.domains and image.remotePatterns configurations to restrict remote image fetching as much as possible.

Useful 0 Not Useful 0